1. Field of the Invention
At least one embodiment of the invention relates to a sensor for temperature changes at electrode poles, in particular electrode poles on an implantable stimulation electrode line for a heart stimulator, implantable pulse generator (IPG), cardioverter/defibrillator (ICD) or the like.
2. Description of the Related Art
Such implantable medical apparatuses are for example implantable defibrillators (ICDs) or heart pacemakers, which can emit electrical stimulation pulses via electrode lines to cardiac tissue (myocardium) or can detect electrical potentials in the heart tissue via adequate sensors. Other implants such as e.g. neurostimulators serve for stimulating other tissues. In connection with heart pacemakers it is know that they provide self-actingly automatic aftercare, e.g. as so-called cron jobs, i.e. perform self-tests which are preprogrammed with respect to sequence and time and during which, in accordance with today's guidelines, certain parameters such as e.g. stimulus threshold, electrode impedance, battery voltage, signal amplitudes etc. are detected. For this purpose, the test unit controlled by the control unit is used.
Implantable heart pacemakers or defibrillators are typically connected to electrode lines for the electrostimulation which have the disadvantage that the electrical conductor of the latter can heat up in a nuclear spin tomograph (also referred to as magnetic resonance tomograph) because the alternating magnetic fields present in the nuclear spin tomograph induce significant electrical currents in the electrical conductor. Also, such induced currents can be emitted via electrode poles of the electrode line to surrounding tissue and thus, for example, can cause undesirable heating of the tissue.
In fact, it is typical that at least one stimulation electrode line is connected to implantable heart pacemakers or defibrillators (hereinafter also designated as heart stimulators or IPGs (implantable pulse generator)), wherein said stimulation electrode line has a standardized electrical connector at its proximal end provided for connecting to the heart pacemaker or defibrillator and has one or a plurality of electrode poles at its distal end provided for placement in the heart. Such an electrode pole serves for emitting electrical pulses to the tissue (myocardium) of the heart and/or for sensing electrical fields so as to be able within the so-called sensing to sense an activity of a heart. For these purposes, electrode poles typically form electrically conductive surface sections of an electrode line. Electrode poles are typically provided as annular electrode in the form of a ring around the electrode line or in the form of a tip electrode at the distal end of the electrode line. The electrode poles are connected in an electrically conductive manner via one or a plurality of electrical conductors to contacts of the electrical connector of the electrode line at the proximal end of the electrode line. Thus, one or a plurality of electrical conductors run between the contacts of the electrical connector at the proximal end of the electrode line and the electrode poles at the distal end of the electrode line, wherein said electrical conductors electrically connect the one or a plurality of electrode poles to one or a plurality of the contacts. These electrical conductors can be used, on the one hand, for transmitting stimulation pulses to the electrode poles and, on the other, for transmitting electrical signals recorded by means of the electrode poles to the proximal end of the electrode line.
On the other hand, the electrode can also dissipate heat generated by currents induced in the electrode line to the surrounding body liquid or the surrounding tissue.
There are already different solutions in existence for reducing the MRT-induced electrode heating; however, primarily with modified electrodes. The temperature sensor, which is often required, is sometimes used.
Currently, the application of an MRT examination in case of patients with an IPG is contrainduced. The problems arising in the environment of the MRT are mainly heating of the electrode tip caused by the strong alternating electromagnetic magnetic field in the MRT.
Approaches to a solution relate primarily to the modification of the electrode; thus, e.g., the use of band-pass filters in the electrode is described. The disadvantages of such a solution, besides the constructional efforts, are primarily the interruption of the therapy-relevant electrode line with resistors, inductive and capacitive components and associated with that, a possible impairment of the therapy function such as, e.g., the emission of high-frequency signals (hemodynamic sensors, in short HDS, or closed loop stimulation, in short CLS, current pulses with steep edges, etc.). In addition, the reliability of the electrode line interrupted by the bandstop filter is reduced by the additional interfaces and thus, a potential source of errors for the failure of such an electrode is created.